Is 100,000 faces a big render? How can I reduce it?
100,000 is a lot of faces on a slow computer, but not too many on a fast computer (definitely not unrealistically high). As a general rule, always stay as low-poly as possible for as long as you can, and use a subdivision modifier to add the look of smoothness while maintaining an easy-to-edit lower-poly mesh for edit/weight paint/etc. modes. Don't apply the subdiv modifier unless you have to. If you can get away with it, never apply it. Rigs will live perfectly well underneath or on top of a subdiv modifier. Working like that helps your viewport stay nice and smooth!

In your case--since it seems you've already applied a smooth or two to your model, you may be able to reduce your poly-count by using the decimate modifier, but that's sort of hit or miss and may require a bit of touch-up.